Clone the data-model repository from Chapter 1, Navigating Git:

$ git clone https://github.com/dvaske/data-model.git
$ cd data-model

First, let's figure out the ID of the commit at HEAD:

$ git rev-parse HEAD
34acc370b4d6ae53f051255680feaefaf7f7850d

This can, of course, also be obtained by git log -1 --format=%H, but with the rev-parse command, you don't need all the options. We can also get the current branch from the rev-parse command:

$ git rev-parse --symbolic-full-name HEAD
refs/heads/master 

We can also just get the abbreviated name:

$ git rev-parse --symbolic-full-name --abbrev-ref HEAD
master

We can also get the ID of other refs:

$ git rev-parse origin/feature/2
82cd5662900a50063ff4bb790539fe4a6d470d56 

The rev-parse command can also be used to give some information about the repository, especially the directory structure relative to the current working directory.

We can find the top-level directory from a subdirectory using the following snippet:

$ cd a_sub_directory
$ pwd
/path/to/repo/data-model/a_sub_directory
$ git rev-parse --show-toplevel
/path/to/repo/data-model

We can also get the number of cd .. we need to get to the root directory using the following command:

$ git rev-parse --show-cdup
../

And we can get the relative path from the root directory to the current working directory using the following command:

$ git rev-parse --show-prefix
a_sub_directory/

Finally, we can get Git to show the path to the .git directory:

$ git rev-parse --git-dir
/path/to/repo/data-model/.git

We can check whether the current repository is a bare repository using the following command:

$ git rev-parse --is-bare-repository
false